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Cellulolytic enzyme hydrolysis of lignocellulose biomass to release fermentable sugars is one of the key steps in biofuel refining. Gene expression of fungal cellulolytic enzymes is tightly controlled at the transcriptional level. Key transcription factors such as activator ClrB/CLR2 and XlnR/XYR1, as well as repressor CreA/CRE1 play crucial roles in this process. The putative protein methyltransferase LaeA/LAE1 has also been reported to regulate the gene expression of the cellulolytic enzyme. The formation and gene expression of the cellulolytic enzyme was compared among  Penicillium oxalicum  wild type (WT) and seven mutants, including Δ laeA  (deletion of  laeA ), OE clrB  ( clrB  overexpression), OE clrB Δ laeA  ( clrB  overexpression with deletion of  laeA ), OE xlnR  ( xlnR  overexpression), OE xlnR Δ laeA  ( xlnR  overexpression with deletion of  laeA ), Δ creA  (deletion of  creA ), and Δ creA Δ laeA  (double deletion of  creA  and  laeA ). Results revealed that LaeA extensively affected the expression of glycoside hydrolase genes. The expression of genes that encoded the top 10 glycoside hydrolases assayed in secretome was remarkably downregulated especially in later phases of prolonged batch cultures by the deletion of  laeA . Cellulase synthesis of four mutants Δ laeA , OE clrB Δ laeA , OE xlnR Δ laeA , and Δ creA Δ laeA  was repressed remarkably compared with their parent strains WT, OE clrB , OE xlnR , and Δ creA , respectively. The overexpression of  clrB  or  xlnR  could not rescue the impairment of cellulolytic enzyme gene expression and cellulase synthesis when LaeA was absent, suggesting that LaeA was necessary for the expression of cellulolytic enzyme gene activated by ClrB or XlnR. In contrast to LaeA positive roles in regulating prominent cellulase and hemicellulase, the extracellular β-xylosidase formation was negatively regulated by LaeA. The extracellular β-xylosidase activities improved over 5-fold in the OE xlnR Δ laeA  mutant compared with that of WT, and the expression of prominent β-xylosidase gene  xyl3A  was activated remarkably. The cumulative effect of LaeA and transcription factor XlnR has potential applications in the production of more β-xylosidase.

The Different Roles of Penicillium oxalicum LaeA in the Production of Extracellular Cellulase and β-xylosidase